1. Field of the Invention
The present invention relates to a pressure sensor.
2. Description of the Related Art
As an example of a conventional pressure sensor, a pressure sensor disclosed in Japanese Patent Publication No. 2819783 is known. This pressure sensor is provided with a semiconductor device that is capable of detecting a pressure, a terminal that is connected to the semiconductor device by a bonding wire, a housing having an accommodation space for accommodating the semiconductor device, the bonding wire and the terminal, a diaphragm for sealing the accommodation space, and working fluid that is sealed in the accommodation space and transmits a pressure applied to the diaphragm to the semiconductor device. Fluorine-based oil that is composed of perfluoro polyether is used as the working fluid. In general, silicone-based adhesive is used in this type of the pressure sensor for sealing between the terminal and the housing.
In this pressure sensor, the diaphragm is deformed when a pressure to be detected acts on the diaphragm, and the pressure is transmitted to the semiconductor device by the working fluid. The semiconductor device detects the pressure, a signal of the pressure is sent to the terminal via the bonding wire, and is then sent to other devices by the terminal. In this case, in this pressure sensor, while the fluorine-based oil as the working fluid maintains favorable pressure transmissibility, swelling of the silicone-based adhesive is prevented due to characteristics of fluorine compound and silicone compound. Accordingly, in this pressure sensor, reduction in adhesivity of the silicone-based adhesive is prevented, whereby sealability between the terminal and the housing is maintained and durability is also demonstrated.
Furthermore, a pressure sensor such as that disclosed in Japanese Patent Laid-Open Publication No. 2001-99737 is also known. This pressure sensor is provided with a semiconductor device that is capable of directly detecting a pressure, a terminal that is connected to the semiconductor device by a bonding wire, and a housing having an accommodation space for accommodating the semiconductor device, the bonding wire, and the terminal, and but is not provided with the aforementioned diaphragm. Moreover, the semiconductor device, the bonding wire, and the terminal are buried in fluorine-based gel that is tilled in the accommodation space as the working fluid, and further, an upper portion of then terminal and the housing are coated with fluorine-based adhesive.
In this pressure sensor, when a pressure to be detected acts on the surface of the fluorine-based gel, the pressure is transmitted to the semiconductor device by the fluorine-based gel. The semiconductor device detects the pressure, a signal of the pressure is sent to the terminal via the bonding wire, and is then sent to other devices by the terminal. In this case, in this pressure sensor, the fluorine-based gel and the fluorine-based adhesive demonstrate durability by being exposed to gasoline vapor, water vapor, or the like.
However, since the pressure sensor disclosed in Japanese Patent Publication No. 2819783 uses expensive fluorine-based oil as the working fluid, a large amount of the fluorine-based oil is used, thus causing an increase in the manufacturing cost. If low-cost silicone-based oil is used as the working fluid instead of the fluorine-based oil, since the terminal and the housing are sealed by the silicone-based adhesive, the silicone-based adhesive swells due to joint characteristics of silicone resin, thus reducing adhesivity. As a result, sealing between the terminal and the housing becomes insufficient, thereby causing a concern about durability.
Furthermore, in the pressure sensor disclosed in Japanese Patent Laid-Open Publication No. 2001-99737 uses both fluorine-based gel and fluorine-based adhesive for protection from outside environment. Therefore, the manufacturing cost increases.